Polypropylene and method for preparing the same

ABSTRACT

The present disclosure relates to a polypropylene for injection having a high content of ultra-high molecular weight and excellent rigidity, and a method for preparing the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 16/635,730 filed Jan. 31, 2020, a national phase entry under 35U.S.C. § 371 of International Application No. PCT/KR2018/013198 filedNov. 1, 2018, which claims priority from Korean Patent Application No.10-2017-0160625 filed Nov. 28, 2017 and Korean Patent Application No.10-2018-0132203 filed Oct. 31, 2018, all the disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a polypropylene with a high content ofultra-high molecular weight and excellent rigidity for injection, and amethod for preparing the same.

BACKGROUND OF ART

Recently, polyolefin products with low specific gravity have beendeveloped as a substitute for plastics or metals with high specificgravity in order to lighten automobiles. In this process, polyolefinproducts with higher strength are increasingly required.

Polyolefins are being converted more and more into polypropyleneproducts (mPP) with less odor and low elution characteristics producedby using metallocene catalysts, although products produced by usingZiegler-Natta catalysts are the mainstream.

That is, olefin polymerization catalyst systems may be divided intoZiegler-Natta and metallocene catalyst systems, and these highly activecatalyst systems have been developed in accordance with theircharacteristics. The Ziegler-Natta catalyst has been widely applied tocommercial processes since it was developed in the 1950's. However,since the Ziegler-Natta catalyst is a multi-active site catalyst inwhich a plurality of active sites are mixed, it has a feature that aresulting polymer has a broad molecular weight distribution. Also, sincea compositional distribution of comonomers is not uniform, there is aproblem that it is difficult to obtain desired physical properties.

On the other hand, the metallocene catalyst includes a main catalysthaving a transition metal compound as a main component and anorganometallic compound cocatalyst having aluminum as a main component.Such a catalyst is a single-site catalyst which is a homogeneous complexcatalyst, and offers a polymer having a narrow molecular weightdistribution and a uniform compositional distribution of comonomers, dueto the single site characteristics. The stereoregularity,copolymerization characteristics, molecular weight, crystallinity, etc.of the resulting polymer may be controlled by changing a ligandstructure of the catalyst and polymerization conditions.

However, as the product to which the metallocene catalyst is applied hasa narrow MWD characteristic, the content of ultra-high molecular weightis low and there is a limit in increasing the injection rigidity.Therefore, it is necessary to develop a new polypropylene with a highcontent of ultra-high molecular weight and a low content of lowmolecular weight in order to solve this problem.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

Accordingly, the present disclosure is to provide a polypropylene forinjection, specifically a homo-polypropylene, with a high content ofultrahigh molecular weight and a low content of low molecular weight,which can improve injection rigidity of a product.

The present disclosure is also to provide a method for preparing thehomo-polypropylene for injection which is excellent in rigidity bypolymerization under a low hydrogen input condition using a specificmetallocene catalyst having high hydrogen reactivity.

Technical Solution

The present disclosure provides a homo-polypropylene satisfying thefollowing conditions:

(1) a weight average molecular weight is 150,000 to 200,000 g/mol and amolecular weight distribution is 2.4 or less, when measured by GPC;

(2) in a GPC curve in which x-axis is log Mw and y-axis is dw/d log Mw,an integral value in the region where Log Mw is 4.5 or less is 8% orless of an integral value of the entire x-axis;

(3) in a GPC curve in which x-axis is log Mw and y-axis is dw/d log Mw,an integral value in the region where Log Mw is 6 or more is 0.95% ormore of an integral value of the entire x-axis; and

a residual stress ratio is 0.20% or more.

In addition, the present disclosure provides a method for preparing thehomo-polypropylene, including a step of continuously polymerizingpropylene monomers in the presence of a catalyst composition containing0.1 to 5.0 wt % of a compound represented by the following ChemicalFormula 1 under a hydrogen input of 200 ppm or less:

wherein, in Chemical Formula 1,

M is a group 4 transition metal,

X₁ and X₂ are the same as or different from each other, and are eachindependently a halogen,

A is silicon or germanium,

R₁ and R₂ are the same as or different from each other, and are eachindependently a C₁₋₂₀ alkyl or a C₆₋₂₀ aryl, and

R₃ and R₄ are the same as or different from each other, and are eachindependently a C₇₋₄₀ alkylaryl.

Advantageous Effects

According to the present disclosure, it is possible to provide a rigidpolypropylene for injection, specifically a homo-polypropylene, having ahigh content of ultrahigh molecular weight and a low content of lowmolecular weight with a narrow molecular weight distribution by using aspecific metallocene catalyst with high hydrogen reactivity andpolymerizing it under a low hydrogen input condition. Therefore, thepresent disclosure is useful for providing a target MI product havingexcellent physical properties.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The terms used in this description are just for explaining exemplaryembodiments, and are not intended to restrict the present invention. Thesingular expression may include the plural expression unless it isdifferently expressed contextually. It must be understood that the word“include”, “equip”, or “have” in the present description is only usedfor designating the existence of characteristics, steps, components, orcombinations thereof, and does not exclude the existence or thepossibility of addition of one or more different characteristics, steps,components, or combinations thereof beforehand.

The present invention may be variously modified and have various forms,and specific examples of the present invention will be explained below.However, it is not intended to limit the present invention to thespecific examples, and it must be understood that the present inventionincludes all modifications, equivalents, or replacements within thespirit and technical scope of the present invention.

Hereinafter, the homo-polypropylene for injection according to preferredembodiment of the present disclosure, and the method for preparing thesame, will be described in more detail.

According to an embodiment of the present disclosure, ahomo-polypropylene satisfying the following conditions is provided:

(1) a weight average molecular weight is 150,000 to 200,000 g/mol and amolecular weight distribution is 2.4 or less, when measured by GPC;

(2) in a GPC curve in which x-axis is log Mw and y-axis is dw/d log Mw,an integral value in the region where Log Mw is 4.5 or less is 8% orless of an integral value of the entire x-axis;

(3) in a GPC curve in which x-axis is log Mw and y-axis is dw/d log Mw,an integral value in the region where Log Mw is 6 or more is 0.95% ormore of an integral value of the entire x-axis; and

a residual stress ratio is 0.20% or more.

Generally, it is known that the higher the molecular weight of thepolymer, the better the mechanical properties. However, when the polymeris prepared by using a metallocene catalyst, MWD becomes narrower, sothat an ultra-high molecular weight content and injection rigiditybecome low.

Accordingly, the present disclosure is intended to provide apolypropylene for injection having a high content of ultra-highmolecular weight and a content of low molecular weight with improvedinjection rigidity, and a method for preparing the same. Herein, thepolypropylene provided by the present disclosure may be ahomo-polypropylene.

More specifically, the homo-polypropylene according to one embodiment ofthe present disclosure has a weight average molecular weight of 150,000to 200,000 g/mol and a molecular weight distribution (MWD=Mw/Mn) of 2.4or less, when measured by GPC. That is, the present disclosure caneasily prepare a polypropylene having a low molecular weight of lessthan 200,000 as well as a polypropylene having a molecular weight of200,000 or more while satisfying a narrow molecular weight distributionof 2.4 or less. Herein, the low molecular weight polypropylene in thisdisclosure may include a polypropylene having Mw of less than 50,000,and preferably Mw of 40,000 to 30,000 or less. Further, in the presentdisclosure, the ultra-high molecular weight polypropylene may include apolypropylene having Mw of 500,000 or more, preferably Mw of 800,000 to1,000,000 or more. The molecular weight may be defined by a criterionthat defines integral values (Log Mw 4.5 or less, Log Mw 6.0 or more) onthe GPC.

Therefore, the homo-polypropylene of the present disclosure has a lowmolecular weight of 150,000 to 200,000 and a narrow molecular weightdistribution, so that exhibits excellent rigidity upon injection. Morepreferably, the molecular weight distribution of the homo-polypropylenemay be 2.0 to 2.4, more specifically 2.2 to 2.4.

In addition, the present disclosure provides a homo-polypropylene havingan increased content of an ultra-high molecular region by an additionalreaction between double-bond chain ends of the polymer in order toenhance injection rigidity. This homo-polypropylene is characterized inthat an integral value in the region where Log Mw is 4.5 or less is 8%or less of an integral value of the entire x-axis, in a GPC curve inwhich the x-axis is log Mw and the y-axis is dw/d log Mw. In addition,the homo-polypropylene is characterized in that an integral value in theregion where Log Mw is 6 or more is 0.95% or more of an integral valueof the entire x-axis, in a GPC curve in which x-axis is log Mw andy-axis is dw/d log Mw. In the above GPC curve, the logarithm of themolecular weight and the mass fraction of the homo-polypropylene aremeasured by GPC, and shown by the x-axis and y-axis. In the above, Mwrefers to a weight-average molecular weight.

Also, as described above, as the content of the ultra-high molecularregion of the homo-polypropylene increases, linking polymers between thechains increase compared with the conventional polymer. Therefore, theresidual stress ratio of the homo-polypropylene is increased to have avalue of 0.20% or more. More preferably, the residual stress ratio maybe 0.25% or more and 0.5% or less. The increase in the residual stressratio leads to improvement of injection strength, however, when theresidual stress ratio is excessively high, workability may be lowered.Therefore, the residual stress ratio is preferably within the aboverange.

The residual stress ratio can be confirmed by a rheological propertytest. A stress relaxation test is performed by applying a large strainto the homo-polypropylene, and the residual stress ratio may be measuredaccording to the following Equation 1.Residual stress ratio=(RS₁/RS₀)*100  [Equation 1]

In Equation 1, RS₀ is a residual stress at any point (to) of less than0.05 seconds after applying 200% strain to the homo-polypropylene at235° C., and RS₁ is a residual stress at any point (t₁) between 0.05seconds and 1.50 seconds after applying 200% strain to thehomo-polypropylene at 235° C.

When the residual stress ratio of the homo-polypropylene according tothe above-mentioned Equation 1 is 0.20% or less, there is a problem thatan increasing effect of injection strength is low. Also, when the ratiois too high, there is a problem that workability becomes low. Therefore,the upper limit is preferably 0.5% or less.

In the above Equation 1, RS₀ represents a residual stress immediatelyafter applying 200% strain to the homo-polypropylene at 235° C. (forexample, at any point (to) of less than 0.05 seconds). In addition, RS₁represents a residual stress within about 1.5 seconds after to under thesame condition as RS₀ (for example, at any point (t₁) between 0.05seconds to 2.0 seconds).

Specifically, in Equation 1, to may be 0.01 seconds, 0.015 seconds, 0.02seconds, 0.025 seconds, 0.03 seconds, 0.035 seconds, 0.04 seconds, or0.045 seconds. In addition, t₁ may be 0.05 seconds, 0.10 seconds, 0.20seconds, 0.30 seconds, 0.40 seconds, 0.50 seconds, 0.60 seconds, 0.70seconds, 0.80 seconds, 0.90 seconds, 1.00 seconds, 1.10 seconds, 1.20seconds, 1.30 seconds, 1.40 seconds, 1.50 seconds, 1.60 seconds, 1.70seconds, 1.80 seconds, 1.90 seconds, or 2.00 seconds. Preferably, to is0.02 seconds and t₁ is 1.00 seconds in the above Equation 2, in order toeasily obtain effective data in the measurement of the residual stress.

In addition, the homo-polypropylene may have tensile strength at yieldof 350 to 400 kg/cm², flexural strength of 480 to 520 kg/cm², and aflexural modulus of 15,500 to 16,800 kg/cm². These are much highervalues compared with a conventional Ziegler-Natta catalyzed homo-PP ormetallocene catalyzed homo-PP.

The flexural strength and flexural modulus of the homo-polypropylenerefer to values measured by ASTM D790 and are well known in the art. Thetensile strength of the homo-polypropylene refers to a value measured byASTM D638 and is well known in the art.

The homo-polypropylene according to one embodiment of the presentdisclosure having the above-mentioned physical properties can beprepared by polymerizing propylene monomers in the presence of acatalyst composition containing a specific metallocene compound as acatalytically active component under a condition of low hydrogen input.

More specifically, according to another embodiment of the presentdisclosure, a method for preparing the homo-polypropylene of claim 1 canbe provided, wherein the method includes a step of continuouslypolymerizing propylene monomers in the presence of a catalystcomposition containing 0.1 to 5.0 wt % of a compound represented by thefollowing Chemical Formula 1 under a hydrogen input of 200 ppm or less:

wherein, in Chemical Formula 1,

M is a group 4 transition metal,

X₁ and X₂ are the same as or different from each other, and are eachindependently a halogen,

A is silicon or germanium,

R₁ and R₂ are the same as or different from each other, and are eachindependently a C₁₋₂₀ alkyl or a C₆₋₂₀ aryl, and

R₃ and R₄ are the same as or different from each other, and are eachindependently a C₇₋₄₀ alkylaryl.

In the present disclosure, the specific metallocene catalyst of ChemicalFormula 1 having high hydrogen reactivity is used to prepare a target MIproduct under a low hydrogen input. According to the present disclosure,the polymerization proceeds under a low hydrogen content condition,thereby inducing an additional reaction between the double-bond chainends to prepare a homo-polypropylene having a high content of ultra-highmolecular weight.

As a result of measuring rheological properties and injection propertiesof the homo-polypropylene having a high content of ultra-high molecularweight prepared by this method, it can be confirmed that rigidity isimproved. In addition, the present disclosure can provide ahomo-polypropylene having a low content of low molecular weight.

Meanwhile, unless otherwise specified herein, the following terms may bedefined as follows.

The halogen may be fluorine (F), chlorine (Cl), bromine (Br), or iodine(I).

The C₁₋₂₀ alkyl group may be a linear, branched, or cyclic alkyl group,more preferably a linear or branched alkyl group. Specifically, theC₁₋₂₀ alkyl group may be a C₁₋₁₅ linear alkyl group; a C₁₋₁₀ linearalkyl group; a C₁₋₅ linear alkyl group; a C₃₋₂₀ branched or cyclic alkylgroup; a C₃₋₁₅ branched or cyclic alkyl group; or a C₃₋₁₀ branched orcyclic alkyl group. More specifically, the C₁₋₂₀ alkyl group may be amethyl group, an ethyl group, an n-propyl group, an iso-propyl group, ann-butyl group, an iso-butyl group, a tert-butyl group, an n-pentylgroup, an iso-pentyl group, a neo-pentyl group, a cyclohexyl group, orthe like.

The C₆₋₂₀ aryl may be a monocyclic, bicyclic, or tricyclic aromatichydrocarbon. Specifically, the C₆₋₂₀ aryl may be phenyl, naphthyl,anthracenyl, or the like.

The C₇₋₄₀ alkylaryl may include substituents in which at least onehydrogen of the aryl is substituted with C₁₋₂₀ alkyl. Specifically, theC₇₋₄₀ alkylaryl may be methylphenyl, ethylphenyl, n-propylphenyl,iso-propylphenyl, n-butylphenyl, iso-butylphenyl, tert-butylphenyl,cyclohexylphenyl, or the like.

The catalyst composition used for preparing the homo-polypropyleneaccording to one embodiment of the present disclosure includes thecompound of Chemical Formula 1 as a single catalyst. As a result, themolecular weight distribution can be remarkably narrowed as comparedwith homo-polypropylenes prepared by using the conventional catalystcomposition containing two or more catalysts.

In Chemical Formula 1, A may be silicon. The substituents of A, R₁, andR₂, are the same in terms of improving solubility and supportingefficiency, and may be a C₁₋₁₀ alkyl group, more specifically a C₁₋₆linear or branched alkyl, or a C₁₋₄ linear or branched alkyl, even morespecifically a methyl, ethyl, or tert-butyl, respectively.

In addition, both of the two indenyl groups, which are ligands, aresubstituted with different functional groups, isopropyl and methyl, at aposition 2, thereby exhibiting higher hydrogen reactivity than acatalyst having two identical indenyl groups. Thus, it can provide adesired MI product even under a low hydrogen condition.

Preferably, R₃ and R₄ may each independently be a phenyl groupsubstituted with a C₁₋₆ branched alkyl group, and more specifically, aphenyl group substituted with a C₃₋₆ branched alkyl group such astert-butylphenyl. The substituting position of the alkyl group withrespect to the phenyl group may be a position of R₃ or R₄ bonded to theindenyl group, or a position 4 corresponding to a para position.

In the above Chemical Formula 1, X₁ and X₂ may each independently bechloro.

A representative example of the compound represented by the aboveChemical Formula 1 may be any one of the following structures:

Further, when preparing a homo-polypropylene in the present disclosure,a hydrogen input can be reduced to 200 ppm or less by using the catalystof a compound represented by Chemical Formula 1.

Therefore, the present disclosure can easily prepare a polypropylenehaving a low molecular weight of less than 200,000 as well as apolypropylene having a molecular weight of 200,000 or more whilesatisfying a narrow molecular weight distribution of 2.4 or less.

In addition, the homo-polypropylene may be prepared by a continuouspolymerization process in which a catalyst composition containing thecompound represented by Chemical Formula 1 and propylene are used, andbrought into contact under a low hydrogen gas content.

Specifically, the hydrogen gas may be charged at a low content of about200 ppm or less, about 100 to about 200 ppm, or about 100 to about 180ppm, based on a total weight of the propylene. Even when the hydrogengas content is low, the catalyst of the present disclosure has highhydrogen reactivity and thus exhibits sufficient catalytic activity.Therefore, the molecular weight distribution of the preparedhomo-polypropylene can be narrowed, and a homo-polypropylene having ahigh content of ultra-high molecular weight can be prepared.

The homo-polypropylene can be prepared by a continuous polymerizationprocess. For example, various polymerization processes known for thepolymerization of olefinic monomers such as a continuous gas phasepolymerization process, a solution polymerization process, a bulkpolymerization process, a suspension polymerization process, a slurrypolymerization process, or an emulsion polymerization process may beapplied. Preferably, a continuous gas phase polymerization process or abulk-slurry polymerization process is better in order to obtain auniform molecular weight distribution and to produce commercialproducts.

As a specific example, the polymerization of the present disclosure canbe carried out according to a continuous slurry polymerization methodusing a prepolymerization reactor and a loop reactor.

This method of the present disclosure may use a reaction apparatus inwhich a prepolymerization reactor and a loop reactor are continuouslyprovided, and a catalyst composition containing 0.1 to 5.0 wt % of thecompound of Chemical Formula 1.

More preferably, the method for preparing the homo-polypropylene mayinclude steps of:

introducing a catalyst composition containing 0.1 to 5.0 wt % of acompound represented by Chemical Formula 1 and propylene monomers into aprepolymerization reactor;

continuously transferring the mixture of the catalyst composition andthe propylene monomers introduced into the prepolymerization reactor toa loop reactor; and

polymerizing the propylene monomers in the loop reactor into which 200ppm or less of hydrogen is charged.

In the present disclosure, the catalyst composition containing thecompound of Chemical Formula 1 is prepared and then introduced into aprepolymerization reactor together with the propylene monomers to carryout a prepolymerization in which the compound of Chemical Formula 1 isfirst contacted with the propylene monomers.

Thereafter, the prepolymerized mixture of the compound of ChemicalFormula 1 and the propylene monomers is transferred to a loop reactorconnected to the prepolymerization reactor, and main polymerization iscarried out in the loop reactor. At the time of the main polymerization,a device for charging hydrogen into the loop reactor may be provided.

Herein, the catalyst composition containing the compound of ChemicalFormula 1 may be introduced into the reactor in the form of a dispersionsolution (in the form of a mud catalyst) using a dispersant. Thus, uponintroduction into the polymerization reactor, the catalyst compositionmay be a dispersion solution further containing a dispersant in additionto the catalyst composition containing 0.1 to 5 wt % of the compound ofChemical Formula 1. The dispersant may be a mixed solution of an oil anda grease. The oil may be a mineral oil.

According to a preferred embodiment, the present disclosure may firstprepare a catalyst composition containing a catalyst (preferably asupported catalyst) having 0.1 to 5 wt % of Chemical Formula 1(hereinafter referred to as a first catalyst composition), and then mixwith the oil/grease, which is a dispersant, to prepare a dispersionsolution (hereinafter referred to as a second catalyst composition)before the polymerization. Therefore, the catalyst compositionintroduced into the prepolymerization reactor and the loop reactor maybe the second catalyst composition.

The second catalyst composition may be a solution prepared so that thecontent of the first catalyst composition is 10 to 30 wt % based on theweight of the oil/grease.

Preferably, the polymerization reaction of the present disclosure usesthe second catalyst composition in which 10 to 30 wt % or 10 to 20 wt %of the first catalyst composition containing the compound of ChemicalFormula 1 is dispersed in the mixture of oil and grease. When thecontent of the first catalyst composition in the second catalystcomposition is less than 10 wt %, the gas phase polymerization does notproceed smoothly. When the content of the first catalyst compositionexceeds 30 wt %, the polymerization reaction is difficult to control.

It is also preferable that the catalyst composition and the propylenemonomers stay in the prepolymerization reactor for 5 to 10 minutes. Theprepolymerization reactor may be at a temperature of 0 to 20° C. and apressure of 10 to 30 kgf/cm².

It is preferable that the catalyst composition and the propylenemonomers stay in the loop reactor for 50 to 120 minutes.

The polymerization reaction in the loop reactor may be carried out at atemperature of about 40 to 110° C. or about 60 to 100° C., and apressure of about 1 to 100 kgf/cm².

Further, the polymerization may be carried out for 50 minutes to 120minutes.

In the polymerization reaction, the catalyst may be used in a dissolvedor diluted form in a solvent such as pentane, hexane, heptane, nonane,decane, toluene, benzene, dichloromethane, chlorobenzene, and the like.Herein, the solvent may be treated with a small amount of alkylaluminumto remove a small amount of water, air, or the like which can adverselyaffect the catalyst.

Meanwhile, the compound of Chemical Formula 1 can be synthesized byapplying known reactions, and a more detailed synthesis method can bereferred to the following examples.

The compound of Chemical Formula 1 may be used as a single component orin the form of a supported catalyst supported on a support.

The support may have hydroxy groups on its surface. Preferably, thesupport may have both the highly reactive hydroxyl group and siloxanegroup, which is dried and from which moisture is removed from thesurface. For example, silica, silica-alumina, or silica-magnesia, whichis dried at a high temperature, can be used, and it may usually containoxides, carbonates, sulfates, or nitrates such as Na₂O, K₂CO₃, BaSO₄,Mg(NO₃)₂, and the like.

The support is preferably dried at 200 to 800° C., more preferably at300 to 600° C., and most preferably at 400 to 600° C. If the dryingtemperature of the support is lower than 200° C., it contains too muchmoisture so that moisture on the surface reacts with the cocatalyst. Ifthe drying temperature is higher than 800° C., pores on the surface ofthe support are combined with each other to reduce the surface area, andmany hydroxyl groups are lost on the surface, leaving only siloxanegroups. Thus, the reactive sites with cocatalyst are reduced, which isnot preferable.

The amount of hydroxyl groups on the surface is preferably 0.1 to 10mmol/g, and more preferably 0.5 to 1 mmol/g. The amount of hydroxygroups may be controlled by the preparation method, the preparationconditions, or the drying conditions such as temperature, time, vacuum,or spray drying of the support.

If the amount of hydroxyl groups is less than 0.1 mmol/g, reactive siteswith the cocatalyst are reduced. If the amount of hydroxyl groups ismore than 10 mmol/g, it is not desirable because it may be caused bymoisture besides the hydroxyl groups present on the surface of supportparticles.

When supported on the support, a weight ratio of the compound ofChemical Formula 1 to the support is preferably 1:1 to 1:1000. When thesupport and the compound of Chemical Formula 1 are contained within theabove weight ratio, they exhibit appropriate activity of the supportedcatalyst, which may be advantageous in terms of maintaining catalyticactivity and economical efficiency.

In addition, when the above cocatalyst is supported, the content thereofmay be 8 to 25 mmol, preferably 10 to 20 mmol, per 1 weight of thesupport, for example, 1 g of silica.

In addition, in the above catalyst composition, the compound representedby Chemical 1 may further include a cocatalyst in addition to thesupport in terms of improving the activity and stability. The cocatalystmay include at least one compound represented by the following ChemicalFormula 2, 3, or 4:—[Al(R₁₁)—O]_(m)—  [Chemical Formula 2]

wherein, in Chemical Formula 2,

R₁₁ are the same as or different from each other, and each isindependently a halogen; a C₁₋₂₀ hydrocarbon; or a C₁₋₂₀halogen-substituted hydrocarbon; and

m is an integer of 2 or more,J(R₁₂)₃  [Chemical Formula 3]

wherein, in Chemical Formula 3,

R₁₂ is as defined in Chemical Formula 2; and

J is aluminum or boron,[E-H]⁺[ZA₄]⁻ or [E]⁺[ZA₄]⁻  [Chemical Formula 4]

wherein, in Chemical Formula 4,

E is a neutral or cationic Lewis base,

H is a hydrogen atom;

Z is a Group 13 element; and

each A is the same as or different from each other, and each isindependently a C₆₋₂₀ aryl or C₁₋₂₀ alkyl group, of which one or morehydrogen atoms are substituted or unsubstituted with a halogen, a C₁₋₂₀hydrocarbon, alkoxy, or phenoxy.

Examples of the compound represented by Chemical Formula 2 may includemethylaluminoxane, ethylaluminoxane, isobutylaluminoxane,butylaluminoxane, and the like, and a more preferred compound ismethylaluminoxane.

Examples of the compound represented by Chemical Formula 3 may includetrimethylaluminum, triethylaluminum, triisobutylaluminum,tripropylaluminum, tributylaluminum, dimethylchloroaluminum,triisopropylaluminum, tri-s-butylaluminum, tricyclopentylaluminum,tripentylaluminum, triisopentylaluminum, trihexylaluminum,trioctylaluminum, ethyldimethylaluminum, methyldiethylaluminum,triphenylaluminum, tri-p-tolylaluminum, dimethylaluminummethoxide,dimethylaluminum methoxide, trimethylboron, triethylboron,triisobutylboron, tripropylboron, tributylboron, and the like, and amore preferred compound is selected from trimethylaluminum,triethylaluminum, and triisobutylaluminum.

Examples of the compound represented by Chemical Formula 4 may includetriethylammonium tetraphenylboron, tributylammonium tetraphenylboron,trimethylammonium tetraphenylboron, tripropylammonium tetraphenylboron,trimethylammonium tetra(p-tolyl)boron, trimethylammoniumtetra(o,p-dimethylphenyl)boron, tributylammoniumtetra(p-trifluoromethylphenyl)boron, trimethylammoniumtetra(p-trifluoromethylphenyl)boron, tributylammoniumtetrapentafluorophenylboron, N, N-diethylanilinium tetraphenylboron,N,N-diethylanilinium tetrapentafluorophenylboron, diethylammoniumtetrapentafluorophenylboron, triphenylphosphonium tetraphenylboron,trimethylphosphonium tetraphenylboron, triethylammoniumtetraphenylaluminum, tributylammonium tetraphenylaluminum,trimethylammonium tetraphenylaluminum, tripropylammoniumtetraphenylaluminum, trimethylammonium tetra(p-tolyl)aluminum,tripropylammonium tetra(p-tolyl)aluminum, triethylammoniumtetra(o,p-dimethylphenyl)aluminum, tributylammoniumtetra(p-trifluoromethylphenyl)aluminum, trimethylammoniumtetra(p-trifluoromethylphenyl)aluminum, tributylammoniumtetrapentafluorophenylaluminum, N, N-diethylaniliniumtetraphenylaluminum, N,N-diethylaniliniumtetrapentafluorophenylaluminum, diethylammoniumtetrapentatetraphenylaluminum, triphenylphosphonium tetraphenylaluminum,trimethylphosphonium tetraphenylaluminum, tripropylammoniumtetra(p-tolyl)boron, triethylammonium tetra(o,p-dimethylphenyl)boron,tributylammonium tetra(p-trifluoromethylphenyl)boron, triphenylcarboniumtetra(p-trifluoromethylphenyl)boron, triphenylcarboniumtetrapentafluorophenylboron, and the like.

When the catalyst composition contains both the support and thecocatalyst, it may be prepared by supporting the cocatalyst compound onthe support, and supporting the compound represented by Chemical Formula1 on the support. Herein, the supporting order of the cocatalyst and thecompound of Chemical Formula 1 can be changed, if necessary. In thepreparation of the catalyst composition, a hydrocarbon-based solventsuch as pentane, hexane, heptane, or the like, or an aromatic solventsuch as benzene, toluene, or the like, may be used as a reactionsolvent.

In the catalyst composition of the present disclosure, for example, themetallocene supported catalyst containing the compound of ChemicalFormula 1 can be prepared by reacting a silica support with acocatalyst, removing solvents from the upper part after theprecipitation, washing with solvents, and then adding a catalystprecursor. Accordingly, the metallocene supported catalyst of thepresent disclosure may have a structure in which analkylaluminoxane-based cocatalyst and a metallocene compound representedby the following Chemical Formula 1 are sequentially supported on asupport.

In the method for preparing the supported metallocene catalyst of thepresent disclosure, the reaction may proceed under an inert atmosphere.

Hereinafter, preferred examples are provided for better understanding.However, these examples are for illustrative purposes only, and theinvention is not intended to be limited by these examples.

Comparative Examples 1 to 4 and Examples 1 to 3

Preparation of Metallocene Supported Catalyst

Silica gel (SYLOPOL 952X, calcined at 250° C., 100 g) was placed in a 2L reactor under an Ar condition, and 766 mL of methylaluminoxane (MAO)was slowly added thereto at room temperature, and stirred at 90° C. for15 hours. After completion of the reaction, the reaction mixture wascooled down to room temperature, allowed to stand for 15 minutes, anddecanted using a cannula. Thereafter, 400 mL of toluene was added to thereaction product, stirred for 1 minute, allowed to stand for 15 minutes,and the solvent was decanted using a cannula.

Each catalyst (700 μmol) of Table 1 was dissolved in 400 mL of toluene,and the catalyst-containing solution was transferred to the reactorusing a cannula. After stirring at 50° C. for 5 hours, the mixture wascooled down to room temperature and allowed to stand for 15 minutes, andthe solvent was decanted using a cannula. 400 mL of toluene was addedthereto, stirred for 1 minute, allowed to stand for 15 minutes, and thesolvent was removed using a cannula. This solvent-removing process wascarried out twice. Thereafter, 400 mL of hexane was added thereto,stirred for 1 minute, allowed to stand for 15 minutes, and the solventwas decanted using a cannula. Then, the antistatic agent (Atmer 163.3 g)was dissolved in 400 mL of hexane and transferred to the reactor using acannula. The mixture was stirred at room temperature for 20 minutes, andthe reaction product was transferred to a glass filter to remove thesolvent, dried under vacuum for 5 hours, and vacuum-dried at 45° C. for4 hours to obtain respective supported catalysts.

Preparation of Homo-Polpropylene (Manufactured in a Continuous PilotPlant)

Each catalyst composition was mixed with oil/grease to prepare a 16 wt %mixture (in the form of a mud catalyst). Thereafter, the mixture and 20kg/h of propylene were introduced to a pre-polymerization reactor(reactor temperature: 20° C., pressure: 15 kgf/cm²) and left for 8 min,followed by continuously being transferred to a loop reactor.

At this time, hydrogen was introduced into the loop reactor togetherwith propylene in the same amount as in Table 2, and the reactortemperature was maintained at 70° C. to prepare a homo-polypropylene(left in the loop reactor for 2 hours, pressure: 38 kgf/cm²). Aftercompletion of the reaction, unreacted propylene was vented.

TABLE 1 ZN127VS Comp. Ex. 1 Purchased from Lyondellbasell Ziegler-Natta

Comp. Ex. 2 mCat1

Comp. Ex. 3 mCat2

Comp. Ex. 4 mCat3

Example 1 mCat4

Example 2 mCat5

Example 3 mCat6

Experimental Example 1

The properties of the polymers of Examples 1 to 3 and ComparativeExamples 1 to 3 were evaluated by the following methods in aconventional manner.

(1) Weight average molecular weight (Mw) and molecular weightdistribution (MWD, polydispersity index) of the polymer, GPC curve. Theweight average molecular weight (Mw) and the number average molecularweight (Mn) of the polymer were measured using a gel permeationchromatography (GPC, manufactured by Waters). The molecular weightdistribution (PDI) was calculated by dividing the weight averagemolecular weight by the number average molecular weight (results: seeTable 2).

Specifically, a polymer sample was pretreated by dissolving in1,2,4-trichlorobenzene containing 0.0125% BHT at 160° C. for 10 hoursusing PL-SP260 equipment. Then, the number average molecular weight andthe weight average molecular weight were measured by standardizing withpolystyrene at 160° C. using PL-GPC220 equipment. The molecular weightdistribution was represented by the ratio of the weight averagemolecular weight to the number average molecular weight.

(2) Log Mw (<4.5) and Log Mw (>6.0): They were calculated from the aboveGPC curve.

(3) Residual stress ratio

For the homo-polypropylene according to the examples and comparativeexamples, a sample was taken and 200% strain was applied thereto at 235°C., respectively. Thereafter, a change in the residual stress wasmeasured for 10 minutes.

The residual stress was measured using a Discovery Hybrid Rheometer(DHR) from TA Instruments. The sample was sufficiently loaded betweenupper and lower plates with a diameter of 25 mm, and melted at 235° C.Then, the gap was fixed at 1 mm and the residual stress was measured.

Based on the measured residual stress data, the residual stress ratio(RS %) was calculated according to the following Equation 1, and theresults are shown in Table 3 below:Residual stress ratio(Y)=(RS₁/RS₀)*100  [Equation 1]

wherein, in Equation 1, RS₀ is a residual stress at 0.02 seconds (to)after applying 200% strain to a synthetic resin sample at 235° C., andRS₁ is a residual stress at 1.00 seconds (t₁) after applying 200% strainto a synthetic resin sample at 235° C.

(4) Tensile Strength at Yield (kg/cm²): It was measured in accordancewith ASTM D790.

(5) Flexural modulus (kg/cm): It was measured for the homo-polypropyleneof the examples and comparative examples in accordance with ASTM D790.

(6) Flexural Strength (kg/cm²): It was measured for thehomo-polypropylene of the examples and comparative examples inaccordance with ASTM D638.

TABLE 2 H² Catalyst (ppm) MW MWD Note Comp. ZN127VS — 188429 3.00Peroxide Ex. 1 cracking Comp. GmCat1 400 187223 2.32 — Ex. 2 Comp.GmCat2 400 155271 2.37 — Ex. 3 Comp. GmCat3 400 166380 2.34 — Ex. 4 Ex.1 GmCat4 180 174533 2.29 — Ex. 2 GmCat5 180 171200 2.30 — Ex. 3 GmCat6180 160079 2.31 —

The GPC and rheological properties of the polypropylene of the examplesand comparative examples were analyzed by the above-mentioned methods,respectively, and the results are shown in Table 3.

TABLE 3 Residual Log Mw Log Mw stress ratio Catalyst Mw (<4.5)* (>6.0)*(%) Comp. Ex. 1 ZN127VS 188429  9.81% 0.98% 0.04 Cornp. Ex. 2 GmCat1180023  9.91% 0.27% 0.04 Cornp. Ex. 3 GmCat2 155271 10.01% 0.24% 0.03Cornp. Ex. 4 GmCat3 172380  9.96% 0.26% 0.03 Ex. 1 GmCat4 174533  7.81%0.99% 0.26 Ex. 2 GmCat5 171200  7.92% 0.98% 0.28 Ex. 3 GmCat6 168079 7.97% 0.95% 0.25

The injection properties of the polypropylene of the examples andcomparative examples were evaluated by the above-mentioned methods,respectively, and the results are shown in Table 4.

TABLE 4 Tensile Strength Flexural Flexural at Yield Strength ModulusCatalyst (kg/cm²) (kg/cm²) (kg/cm²) Comp. ZN127VS 338 451 15049 Ex. 1Comp. GmCat1 330 450 15100 Ex. 2 Comp. GmCat2 338 467 15363 Ex. 3 Comp.GmCat3 333 449 14950 Ex. 4 Ex. 1 GmCat4 371 510 16500 Ex. 2 GmCat5 373507 16752 Ex. 3 GmCat6 369 506 16625

Referring to Tables 2 to 4, it can be confirmed that Examples 1 to 3 ofthe present disclosure have excellent injection properties with a lowcontent of low molecular weight and a high content of ultra-highmolecular weight, as compared with Comparative Examples 1 to 4.

The invention claimed is:
 1. A method for preparing ahomo-polypropylene, comprising a step of continuously polymerizingpropylene monomers in the presence of a catalyst composition containing0.1 to 5.0 wt % of a compound represented by the following ChemicalFormula 1 under a hydrogen input of 200 ppm or less:

wherein, in Chemical Formula 1, M is a group 4 transition metal, X₁ andX₂ are the same as or different from each other, and each independentlya halogen, A is silicon or germanium, R₁ and R₂ are the same as ordifferent from each other, and each independently a C₁₋₂₀ alkyl or aC₆₋₂₀ aryl, and R₃ and R₄ are the same as or different from each other,and each independently a C₇₋₄₀ alkylaryl, wherein the homo-polypropylenesatisfying the following conditions: (1) a weight average molecularweight is 150,000 to 200,000 g/mol and a molecular weight distributionis 2.4 or less, when measured by GPC; (2) in a GPC curve in which x-axisis log Mw and y-axis is dw/d log Mw, an integral value in the regionwhere Log Mw is 4.5 or less is 8% or less of an integral value of theentire x-axis; (3) in a GPC curve in which x-axis is log Mw and y-axisis dw/d log Mw, an integral value in the region where Log Mw is 6 ormore is 0.95% or more of an integral value of the entire x-axis; and (4)a residual stress ratio is 0.20% or more.
 2. The method for preparingthe homo-polypropylene of claim 1, wherein the method comprises stepsof: introducing the catalyst composition and propylene monomers in aprepolymerization reactor to form a mixture; continuously transferringthe mixture to a loop reactor; and polymerizing the propylene monomersin the loop reactor into which 200 ppm or less of hydrogen is charged.3. The method for preparing the homo-polypropylene of claim 1, whereinR₁ and R₂ are each independently a C₁₋₆ linear or C₃₋₆ branched alkyl.4. The method for preparing the homo-polypropylene of claim 1, whereinR₁ and R₂ are each independently methyl, ethyl, or tert-butyl.
 5. Themethod for preparing the homo-polypropylene of claim 1, wherein R₃ andR₄ are each independently a phenyl group substituted with a C₃₋₆branched alkyl group.
 6. The method for preparing the homo-polypropyleneof claim 1, wherein R₃ and R₄ are each independently a tert-butylphenyl.7. The method for preparing the homo-polypropylene of claim 1, wherein Mis zirconium and A is silicon.
 8. The method for preparing thehomo-polypropylene of claim 1, wherein the compound represented byChemical Formula 1 is supported on a support.
 9. The method forpreparing the homo-polypropylene of claim 1, wherein the catalystcomposition further comprises at least one of a compound represented bythe following Chemical Formula 2, a compound represented by ChemicalFormula 3, or a compound represented by Chemical Formula 4:—[Al(R₁₁)—O]_(m)—  [Chemical Formula 2] wherein, in Chemical Formula 2,each R₁₁ is the same as or different from each other, and independentlya halogen; a C₁₋₂₀ hydrocarbon; or a C₁₋₂₀ halogen-substitutedhydrocarbon; and m is an integer of 2 or more,J(R₁₂)₃  [Chemical Formula 3] wherein, in Chemical Formula 3, each R₁₂is the same as or different from each other, and independently ahalogen; a C₁₋₂₀ hydrocarbon; or a C₁₋₂₀ halogen-substituted hydrocarbonand J is aluminum or boron,[E-H]⁺[ZA₄]⁻ or [E]⁺[ZA₄]⁻  [Chemical Formula 4] wherein, in ChemicalFormula 4, E is a neutral or cationic Lewis base; H is a hydrogen atom;Z is a Group 13 element; and each A is the same as or different fromeach other, and independently a C₆₋₂₀ aryl or C₁₋₂₀ alkyl group, each ofwhich is unsubstituted or substituted with a halogen, a C₁₋₂₀hydrocarbon, alkoxy, or a phenoxy.
 10. The method for preparing thehomo-polypropylene of claim 1, wherein the catalyst composition is adispersion solution further containing a dispersant.
 11. The method forpreparing the homo-polypropylene of claim 2, wherein the mixture staysin the prepolymerization reactor for 5 to 10 minutes.
 12. The method forpreparing the homo-polypropylene of claim 2, wherein the polymerizationof the propylene monomers in the loop reactor is carried out for 10 to120 minutes.
 13. The method for preparing the homo-polypropylene ofclaim 1, wherein the hydrogen input is 100 to 200 ppm.
 14. The methodfor preparing the homo-polypropylene of claim 1, wherein the compoundrepresented by Chemical Formula 1 is one of the following structures:


15. The method for preparing the homo-polypropylene of claim 2, whereinthe prepolymerization reactor is at a temperature of 0 to 20° C. and apressure of 10 to 30 kgf/cm², and the polymerization reaction in theloop reactor is carried out at a temperature of about 40 to 110° C., anda pressure of about 1 to 100 kgf/cm².
 16. The method for preparing thehomo-polypropylene of claim 8, wherein the support has a hydroxyl groupon a surface, and a weight ratio of the compound of Chemical Formula 1to the support is 1:1 to 1:1000.
 17. The method for preparing thehomo-polypropylene of claim 1, wherein the molecular weight distributionmeasured by GPC is 2.0 to 2.4.
 18. The method for preparing thehomo-polypropylene of claim 1, Wherein the homo-polypropylene has atensile strength at yield of 350 to 400 kg/cm², a flexural strength of480 to 520 kg/cm², and a flexural modulus of 15,500 to 16,800 kg/cm².